Why an engine makes more power off a burr finish

[Kevin Johnson]

Someone posted this pic on ST long ago. It's said to be inside an "s" tube of a 727.

Looks a bit like vanes to trip the boundary layer to keep it attached to the curved channel.

Küpper,, D. (1999). A study of the application of air-jet vortex generators to intake ducts. (Unpublished Doctoral thesis, City University London)

http://openaccess.city.ac.uk/7750/1/A_s ... _ducts.pdf

A nice treatment of the subject.

[groberts101]

Flow straightener. Notice they are before the turns. Placed to keep the air from tumbling. Better quality of air control vs chaotic.

Quality not quantity.

Uh..yup. Easy to hog out a port and put a bigger valve in it to increase airflow over the long side. Just a wee bit tougher to improve the flow on the short side. And power gains per CFM of flow improvement are not linear between the two.

[David Redszus]

Flow straightener. Notice they are before the turns. Placed to keep the air from tumbling. Better quality of air control vs chaotic.

Quality not quantity.

I am a bit confused by what you mean by "better quality of air" and "quality not quantity". Isn't the overriding objective to increase the air mass flow? The presence of turbulence serves to reduce mass flow.

[The Radius Kid]

Flow straightener. Notice they are before the turns. Placed to keep the air from tumbling. Better quality of air control vs chaotic.

Quality not quantity.

I am a bit confused by what you mean by "better quality of air" and "quality not quantity". Isn't the overriding objective to increase the air mass flow? The presence of turbulence serves to reduce mass flow.

I *suspect* he misspoke.
It sounds to me like meant to say that quality and good control of airflow will enhance ultimate airflow levels.
In other words,quantity follows quality.
Similar to form follows function.
Let me know if I got it wrong Chad.

[digger]

Personally I think he made no mistake in the words chosen.

[user-9274568]

Personally I think he made no mistake in the words chosen.

Your exactly right.

[The Radius Kid]

Personally I think he made no mistake in the words chosen.

Your exactly right.

So what exactly are you saying?

[user-9274568]

Flow straightener. Notice they are before the turns. Placed to keep the air from tumbling. Better quality of air control vs chaotic.

Quality not quantity.

I am a bit confused by what you mean by "better quality of air" and "quality not quantity". Isn't the overriding objective to increase the air mass flow? The presence of turbulence serves to reduce mass flow.

What???????

So your saying as long as the air get's there your good?

[user-9274568]

I'm not an engineer, but this makes sense... Consider this: Engines don’t burn just fuel, they burn fuel and air. The more air, the more power, and fuel delivery is adjusted accordingly…or so the axiom goes. In reality, air quantity must be equated with air quality, for without proper conditioning of mixtures, combustion efficiency will suffer. More air isn’t always more power.

[David Redszus]

There are at least two parts to this issue.

The first is the ability to flow the greatest mass of air into the engine. Mass of air is the result of air volume x air density. If fuel is present, it reduces the mass of air that can be ingested. The greater the mass of air that can be brought into the combustion chamber, the greater the mass of fuel that can be burned. Turbulence in the induction tube will reduce the air mass that can be ingested but may have other over-riding benefits.

Once the mixture of air and fuel is safely inside the combustion chamber, the combustion process is governed by the three Ts; Time, Temperature and Turbulence. Actually, temperature and turbulence will determine the time required. The combustion period, for a given mixture mass, will determine the pressure that will be developed. That combustion pressure applied to the piston crown and conrod lever, will determine the torque production of that cylinder.

[jmarkaudio]

I think the bottom line is MIXTURE quality, having the air and fuel mixed in a more homogenous mix, leading to more equal distribution. You might get more air in, but if the fuel distribution is more uneven it will likely not make the power, burn the fuel most efficient.

[MadBill]

Re same, a number of builders have reported that a full radius intake seat flows more air but makes less power than one with multiple discrete angles, hypothesized to be due to wall flow liquid fuel being sheared into the airstream by the sharp angles. Additional testing with gaseous fuel could confirm or disprove this...

[David Redszus]

Somewhere, on one of the backroom computers, lives a video clip produced by Mercury Marine that shows a liquid fuel shower flowing past the closing valve. It then shows the spark kernal and developing flame front.

It makes me wonder just how well prepared is the air/fuel mixture with regard to atomazation and evaporation.
In some applications, liquid fuel droplets help cool the piston and chamber surfaces.

[GARY C]

This argument will go on for ever! from what I have seen in 20 years of study is that those who test it find it's advantages and disadvantages and those who have a theory that there is no advantage will never test it!

I can show you a video from my computer that shows a large amount of air flow into the cylinder at TDC but you will still have those that claim it doesn't happen...and probably would refuse to watch the video!

For me I hope the battle rages on because as the behind the scenes spectator...IE: Little Guy/Mystery shopper I get to learn who is bound by theory, who is willing to step out side the box and who will explain the theory while standing out side the box and then show that the biggest problem with most theory's is that they rarely hold true in practice!

[user-9274568]

This argument will go on for ever! from what I have seen in 20 years of study is that those who test it find it's advantages and disadvantages and those who have a theory that there is no advantage will never test it!

I can show you a video from my computer that shows a large amount of air flow into the cylinder at TDC but you will still have those that claim it doesn't happen...and probably would refuse to watch the video!

For me I hope the battle rages on because as the behind the scenes spectator...IE: Little Guy/Mystery shopper I get to learn who is bound by theory, who is willing to step out side the box and who will explain the theory while standing out side the box and then show that the biggest problem with most theory's is that they rarely hold true in practice!

Right on my manifold web page I have a disclaimer that says if you don't want a burr finished manifold, don't buy one from me.....

SRH DISCLAIMER:
For racers or engine builders interested in SRH ported manifolds. We only do burr finish work. We don't polish it smooth as glass. If you don't want a burr finished manifold proven from many dyno sessions, back to back runs, and track times, please don't order one from SRH. You might be disappointed in the looks, BUT NOT THE PERFORMANCE! Which is backed by my guarantee. The circle in the middle is my signature. It's not a tuning aide. It's not for performance. It's for looks, nothing more!